Sealing assemblies for sealing an annular space between an inner member, such as a shaft, and an outlet member, such as a housing, which are rotatable relative to one another, are well known. One general type of sealing assembly is a radial lip seal assembly. Such seal assemblies are widely used in automotive vehicles, including trucks and off-road vehicles, such as farm equipment, and construction vehicles, to keep out dust and dirt and to keep in lubricant. There are substantial variations in the structures of radial lip seal assemblies. However, radial lip seal assemblies commonly include a thin, rigid structural element, commonly known as an outer case member, which extends generally radially inwardly from the housing and which supports a shaft seal (usually elastomeric) that engages an outer cylindrical surface of the shaft, and a radial lip which is carried on the shaft and extends generally radially outwardly. The radial lip aids in keeping out dust and dirt.
While the housing or outer member is usually stationary, and the shaft or inner member is usually rotatable, this is not always the case. For example, a radial lip seal assembly for sealing an annular space between a stationary axle spindle and a rotatable wheel hub (which serves as a housing) surrounding the axle spindle at the outer end of an automotive vehicle axle is well known.
Although presently known radial lip seals keep out dust and dirt to some extent, they still permit appreciable quantities of dust and dirt to reach the shaft seal. As a result, shaft seals have a high failure rate, and most failures are caused by external contamination.